Image forming apparatus and method for operating image forming apparatus

An image forming apparatus, comprising:

• one or more controllers;
• and
• an image former having one or more detachable fixing units,
• wherein:
• the one or more controllers acquire fixing unit information on a fixing unit attached to the image former, and execute a predetermined process, based on the acquired fixing unit information,
• the fixing unit information comprises identification information for uniquely identifying the fixing unit, and
• the predetermined process comprises determining a size of sheets, on which image formation using the fixing unit is permitted, based on the identification information, and determining whether to execute image formation on the sheets, using the image former, based on a result of the predetermined process, wherein
• the one or more controllers:
• in a case that the size of sheets is a first size, permit the execution of image formation on sheets of the first size, and restrict the execution of image formation on sheets other than the first size;
• and
• in a case that a number of times the image formation has been executed on the sheets of the first size becomes greater than a predetermined number, restrict the execution of image formation on the sheets of the first size, and permit the execution of image formation on sheets of a second size, smaller than the first size.